A HEAVY TRANSPORT ON APPROACH TO LGB FLEW AN UNSTABILIZED APPROACH AND GOT A 'GLIDE SLOPE' AURAL WARNING.

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WHILE ON VISUAL APCH TO RWY 30 LGB RECEIVED 'GS' AURAL WARNING DURING LAST 100-150 FT WHILE OVER RWY (2576 FT OF DISPLACED THRESHOLD); TOUCHDOWN WAS AT 1000 FT MARKER ON RWY. REF SPD: 138 KTS; TARGET SPD 143 KTS. AUTOBRAKES SET TO 4. DURING THIS APCH/LNDG; WIND WAS 270 DEGS AT 16 KTS AND A BIT GUSTY. NUMEROUS LIGHT ACFT IN AND AROUND ARPT TFC PATTERN. TWR HAD ADVISED US OF TFC IN L-HAND PATTERN FOR RWY 25L THAT WOULD CROSS OVER US DURING OUR APCH. I WAS PF AND HAD THE AUTOPLT ON AND COUPLED TO THE ILS APCH AS I NORMALLY DO AT THIS ARPT TO AID IN VISUALLY IDENTING TFC WARNINGS ON TCAS. WE HAD AT LEAST 2 AMBER FLASHING WARNING DURING LAST 500 FT OF APCH. APPROX 200 FT AGL; I NOTICED WE WERE DRIFTING L OF CTRLINE; SO I DISCONNECTED THE AUTOPLT AND CORRECTED BACK TO CTR. I THEN LOOKED UP AT TFC ABOUT TO CROSS OVERHEAD (A SMALL CESSNA IN THE PATTERN FOR RWY 25L WHICH WAS ONE OF THE AMBER TCAS ACFT). DURING THIS DISTR; WE ENTER A SINK WHICH TOOK US BELOW GLIDE PATH (FO CALLED 1 DOT LOW). MY FOCUS WAS THEN VISUAL LOOKING AT THE RWY AIM POINT THOUSAND FT MARKERS. WE WERE OVER THE DISPLACED THRESHOLD AND THE GPWS AURAL 'GS' WARNING ACTIVATED. I WAS TOTALLY FOCUSED ON THE VISUAL AIM POINT AND WAS CERTAIN WE WOULD TOUCH DOWN BEYOND THE THRESHOLD; SO I CONTINUED TO LNDG AND WE TOUCHED DOWN AT THE 1000 FT MARKERS. I HAVE FLOWN THIS APCH MANY; MANY TIMES. THERE IS ONLY 6324 FT OF RWY BEYOND THE GS TOUCHDOWN POINT. I HAVE EXPERIENCED TOUCHDOWNS BEYOND THIS POINT (BOTH AS PF AND PLT MONITORING) WHICH RESULTED IN HVY BRAKING TO STOP ON REMAINING RWY. THE 2576 FT OF DISPLACED THRESHOLD IS VERY UNUSUAL FOR A RWY OF THIS LENGTH (10000 FT). I TEND TO FOCUS ON ENSURING WHEELS TOUCH DOWN ON THE 1000 FT MARKERS HERE MORE THAN ANY OTHER ARPT I CAN THINK OF. IT WAS; HOWEVER; THE FIRST TIME I EXPERIENCED THE AURAL 'GS' WARNING. AT ANY OTHER ARPT/APCH I WOULD HAVE NOT HESITATED TO GO AROUND. CONTRIBUTING FACTORS: NUMEROUS TCAS WARNINGS TO THE LGB'S PRACTICE OF ALLOWING ACFT TO CROSS OVERHEAD OF US WHILE ON APCH TO RWY 30 -- IT'S VERY DISTRACTING. SOMEWHAT GUSTY WIND CONDITIONS (WHICH CONTRIBUTED TO OUR SINK BELOW THE GS). THE USUALLY LONG DISPLACED THRESHOLD. THE 6324 FT BEYOND THE GS TOUCHDOWN POINT (SHORT FOR A HVY ACFT).